1. Field of the Invention
The present invention is generally directed to aqueous cement slurries used in oil and gas well operations, and more particularly, to such slurries containing dispersants which function to prevent premature slurry gelation and high viscosity development.
2. Description of the Prior Art
Aqueous cement slurries are commonly utilized in the oil industry in the completion, stimulation and production of oil and gas wells. The most common use of such aqueous cement slurries is in the bonding of conduits such as casing and liners disposed in the well bores to surrounding earth formations. Typically, an aqueous cement slurry is pumped down the inside of a conduit disposed in a well bore to the bottom of the well bore and then upwardly within the annular space between the outside of the conduit and the well bore. Upon hardening, the cement composition bonds the conduit to the earth formations forming the sides of the well bore.
A problem persistently encountered in pumping cement slurries through conduits disposed in well bores involves the premature gelation of the cement slurries whereby the slurries develop high viscosity rendering them difficult or impossible to pump.
Numerous additives have been developed and used heretofore which when combined with aqueous cement slurries function to retard early gelation and viscosity development. For example, U.S. Pat. No. 4,293,342 issued Oct. 6, 1981 discloses additives comprised of lingosulfonate derivatives which are useful as cement slurry gelation retarding agents. While such agents and other prior art dispersants are useful for retarding premature gelation and viscosity development in aqueous cement slurries, there is a continuous demand for more effective and economical such additives.
By the present invention, improved cement slurry dispersants are provided which retard premature gelation and viscosity development in aqueous cement slurries whereby the pumping times of such slurries are increased.